The Puggalapannatti, the Description of Human Types, stands apart from the rest of the Abhidhamma Pitaka by taking as its subject not impersonal mental factors or elements but persons themselves, cataloging different types of individuals according to their spiritual attainment, ethical character and psychological disposition, organized, in a structure that closely echoes the numerically organized Anguttara Nikaya, from single-factor descriptions of a person, someone freed by wisdom, someone freed both ways, upward through steadily larger groupings describing types by two, three and more shared characteristics, culminating in more elaborate tenfold classifications. Its content includes the canonical descriptions of the four stages of awakening recognized in Theravada Buddhism, the stream-enterer, the once-returner, the non-returner and the fully awakened arahant, each defined by exactly which mental defilements have been eliminated and which remain, material that has become foundational to how Theravada Buddhism describes and measures spiritual progress along the path to liberation. Unlike the more purely abstract analysis found in books such as the Dhatukatha or Patthana, the Puggalapannatti retains a recognizably human, almost portrait-like quality, describing recognizable psychological and spiritual types rather than only impersonal categories of momentary phenomena.